Organic electroluminescence devices have advantageous features such as self emission and high-speed response, and are expected for the application to flat panel displays. In particular, since such organic electroluminescence devices were reported that have a dual-layer structure (lamination type) in which a hole-transporting organic thin film (hole transport layer) is laminated on an electron-transporting organic thin film (electron transport layer), organic electroluminescence devices have been attracting attention as a large-area light-emitting device that emits light at a low voltage of 10 V or lower. The organic electroluminescence devices of lamination type have a basic structure of anode/hole transport layer/emission layer/electron transport layer/cathode.
Various attempts have been made to elongate the service life of such organic electroluminescence devices. For example, PTL 1 and other literatures disclose an organic electroluminescence device including an emission layer containing a host material in an amount of 50% by mass or more and a hole transport layer containing the host material in an amount of 5% by mass to 50% by mass or more, wherein the emission layer contains substantially no material other than the host material among the hole transporting materials contained in the hole transport layer.
Also, PTL 2 and other literatures disclose an organic electroluminescence device including a hole injection layer, a hole transport layer and an emission layer each containing a phosphorescent light-emitting material, wherein the hole injection layer contains the phosphorescent light-emitting material in an amount of 10% by mass to 90% by mass and wherein the concentration of the phosphorescent light-emitting material contained in the hole transport layer is lower than that in the hole injection layer and higher than that in the emission layer.
In addition, PTL 3 and other literatures disclose an organic electroluminescence device including a hole injection layer, a hole transport layer, an emission layer and a mixture layer, wherein the mixture layer is disposed between the emission layer and the hole injection layer or the hole transport layer.
However, these organic electroluminescence devices cannot attain high external quantum efficiency although their service life is elongated.
In view of this, keen demand has arisen for development of an organic electroluminescence device exhibiting high external quantum efficiency and a method for producing the organic electroluminescence device.